FRESHWATER

The Water Cycle

There is a continuous movement of WATER from the atmosphere to the earth’s SURFACES and then back to the ATMOSPHERE.

This cycle of water movement is called the WATER CYCLE or the HYDROLOGIC CYCLE.

EVAPOTRANSPIRATION: evaporation and transpiration = organisms giving off water vaporRUNOFF: water flowing into riversGROUNDWATER: water soaking into the groundCONDENSATION: water vapor turning into liquid waterPRECIPITATION: water falling to Earth- snow, rain, etc.

WATER BUDGET:

The continuous CYCLE of evapotranspiration, condensation and precipitation gives the earth its WATER BUDGET.

Expenses: EVAPOTRANSPIRATION, RUNOFFIncome: PRECIPITATION, CONDENSATION

Factors affecting the local water budget:

•TEMPERATURE•VEGETATION•WIND•AMOUNT OF RAIN•DURATION OF RAINY SEASON

**Earth’s water budget as a whole is balanced, but the local water budget

usually is not balanced **

WATER CONSERVATION:Scientists have identified 2 approaches that can be used to ensure there is FRESHWATER for the future. CONSERVATION: antipollution laws; education on water conservation

Finding other supplies of water:DESALINATION: process of removing salt from ocean water.

River Systems

A river system is made up of a MAIN STREAM and all the feeder streams, called TRIBUTARIES, that flow into it.

WATERSHED: land from which water runs into stream (aka drainage basin)DIVIDES: elevated areas of high ground. Separate watersheds

A river system begins to form when local PRECIPITATION exceeds EVAPORATION. The SOIL soaks up as much water as it can. GRAVITY causes excess water to move DOWNSLOPE as RUNOFF.

STREAM EROSION:The path that a stream follows is a CHANNEL.HEADWATER EROSION: lengthening and branching of a streamSTREAM PIRACY: “capture” of one stream by another

CHANNEL EROSION:The edges of a stream that are above water are called BANKS. The part of the stream channel that is below the water level is the BED. A stream gradually becomes WIDER and DEEPER as it erodes.

Stream Loads:Materials that are carried by a stream are known as the STREAM LOAD.

Stream Load Size of Particle Rate of Stream Erosion

Dissolved Load VERY SMALL,

DISSOLVED IN

WATER

SLOW TO NONE

Suspended Load FINE SAND AND

SILTSLOW

Bed loadROCKS &

PEBBLESFAST

POTHOLE: bowl-shaped cavity caused by erosion

DISCHARGE GRADIENT:

A stream’s ability to cut down and widen channel is affected by VELOCITY, STREAM LOAD, and DISCHARGE.

A FAST moving stream carries more SEDIMENT than a slow moving stream.

DISCHARGE: volume of water moved by a streamGRADIENT: steepness of slopeHEADWATERS: beginning of a stream

WIND AND WATER GAPS:Movements of the earth’s crust can RAISE orLOWER the surface of the land, and affect STREAM FLOW.

WIND GAP: Water eroded notch in a mountain through which no water can flow.WATER GAP: Deep notch left where a stream erodes through mountains where the land is uplifted.

STAGES OF A RIVER SYSTEM:

The development of a river is divided into 3 stages - YOUTHFUL, MATURE, and OLD.

YOUTHFUL RIVERS:•Few tributaries•Small volume of water•Not much meandering

MATURE RIVERS:

•More tributaries•More water (larger volume)•Some meandersMeanders – curving of riversOxbow lake – a lake is formed from a meander

Meanders – curving of rivers

Oxbow lake – a lake is formed from a meander

OLD RIVERS:

•Many tributaries•Broad, flat plains•Lots of meanders

REJUVENATED RIVERS:A river that gains steep gradient by some shift in the land

Stream Deposition

The total load a stream can carry is GREATEST when a large VOLUME of water is flowing. When the VELOCITY decreases, the ability of the stream to carry its load also DECREASES. As a result, part of the stream load is DEPOSITED.

DELTA AND ALLUVIAL FANS:

Most of the LOAD carried by a stream is DEPOSITED when the stream reaches a LARGE BODY OF WATER.

DELTA: fan-shaped deposit at mouth of riverALLUVIAL FAN: fan-shaped deposit at bottom of slope on land

DELTA

ALLUVIAL FAN

Delta Alluvial Fan

DEPOSITED IN WATER DEPOSITED ON LAND

MADE OF MUDCOARSE ANGULAR

SAND/GRAVEL

FLAT SURFACE SLOPING LAND

DIFFERENCES

FLOOD DEPOSITS:The SIZE of a stream channel is determined by the average VOLUME of water that flows in the STREAM. The part of the VALLEY FLOOR that may be covered with water during a FLOOD is called the FLOODPLAIN.

SPRING FLOODS: water released by melting snowICE JAMS: ice blocking stream channelsNATURAL LEVEES: deposits along banks of streams 

Why do people choose to live on floodplains?FERTILE SOIL and LOTS OF WATER FOR USE

FLOOD CONTROL:

ARTIFICIAL LEVEES

OVERFLOW CHANNELS

FLOOD CONTROL DAMS

Groundwater & Erosion

Water Beneath the Surface

Water that seeps into the upper layers of the earth’s crust is called GROUNDWATER.90 % of earth’s freshwater is underground.

In the US, groundwater supplies 20 % of the freshwater needs.Amount of groundwater is 50 times greater than that of rivers and streams.

AQUIFER: a body of rock through which large amounts of water can flow and in which much water is stored.

The quality of the aquifer depends on: (2 THINGS)

1. POROSITY - the amount of water that a rock can hold, refers to the amount of open space present•The main influence of porosity is SORTING•Well sorted soil – particles are all the SAME size• Poorly sorted soil – particles are all DIFFERENT sizes

POORLY SORTED MEDIUM SORTED WELL SORTED

The quality of an aquifer depends on:

2. PERMEABILITY - indicates how freely water passes through the open spaces, the spaces must be CONNECTED.

If water cannot flow through the rock, it is said to be IMPERMEABLE. (aka AQUITARD)

GRAVITY pulls water down through the rock until it reaches an impermeable layer. Water then begins to SATURATE the pore spaces above the impermeable rock.

ZONE OF AERATION - area above the impermeable layer where the pore spaces are filled with air.

ZONE OF SATURATION - area directly above the impermeable layer where the pore spaces are filled with water.

WATER TABLE - the upper part of the zone of saturation

Groundwater can be polluted by:  •WASTE DUMPS•LEAKING UNDERGROUND STORAGE TANKS•FERTILIZERS & PESTICIDES•SALTWATER INTRUSION

Groundwater can be conserved by:•MONITOR LEVEL OF GROUNDWATER•RECYCLE USED WATERoPURIFYoPUMP BACK INTO THE GROUND

Two ways that groundwater comes to the surface are:WELL - a hole that is dug below the water table and then pumped to the surface

SPRING - a natural flow of groundwater found where the ground dips below the water table

Wells & Springs:

Two main types of wells and springs:1. ORDINARY - as described above2. ARTESIAN - one through which water

flows freely with no pumping required.

This requires that the water is trapped between two IMPERMEABLE layers. The impermeable layer on top is known as the CAP ROCK. Once the cap rock is penetrated, the water trapped below flows freely to the surface.

The area of the water table around a well often dips down and is known as a CONE OF DEPRESSION.

HOT SPRINGS - groundwater that is heated below ground and then flows to the surface. It is often heated by recent VOLCANIC activity or is near pockets of MAGMA.

Hot springs that erupt periodically are known as GEYSERS. (Ex. OLD FAITHFUL in Yellowstone National Park)

Groundwater and Chemical Weathering:

As water passes through rock, it DISSOLVES minerals. The WARMER the rock and water are, the more minerals that will dissolve.HARD WATER:•Contains minerals (such as calcium, magnesium, iron)•Can damage household appliances

Results of Chemical Weathering by Groundwater:CAVERN - a large underground chamber, hollowed out by the action of waterSINKHOLE - circular depression caused when the roof of a cavern collapses

STALACTITE - cone shaped deposit suspended from the ceiling of a cavernSTALAGMITE - cone shaped deposit built up from the floor of a cavern

Results of Chemical Weathering by Groundwater:NATURAL BRIDGE - an arch of rock formed by groundwater erosion (two open places on either side)KARST TOPOGRAPHY - region where the effects of chemical weathering due to groundwater, such as sinkholes and caverns